The present invention relates generally to arrangements for receiving and emanating electromagnetic signals and, more particularly, to a device integrated antenna arrangement which is usable in resonant and non-resonant modes.
Recent energy crises have highlighted the growing demands placed on traditional sources of power, such as gas and electricity. With rising energy costs, it is desirable to find alternative power sources to augment traditional power sources such as hydroelectric and thermonuclear. Solar energy conversion provides such an alternative by tapping into the readily available power of the sun.
One of the main obstacles preventing the proliferation of solar energy conversion systems is efficiency. Currently available semiconductor solar cell systems are not able to provide the amount of power for the dollar that is possible by traditional power sources. Especially semiconductor solar cells with high energy conversion efficiency (ratio of incident solar power to electrical power out) are expensive. Most solar cell systems are based on semiconductor technology, which can be difficult to scale to the size required for large solar panels. Using the present technology, it is expensive to fabricate a semiconductor-based solar panel which is large enough to replace the traditional sources of power. Moreover, semiconductor devices are generally single bandgap energy devices. This characteristic of semiconductor devices means that no current is produced when a photon having energy less than the bandgap energy is incident on the semiconductor device and, when a photon having energy greater than the bandgap energy is incident on the semiconductor device, only current corresponding to the bandgap energy is produced in the semiconductor device. In other words, the response of the semiconductor device is limited by the bandgap energy. Thus, the semiconductor device does not respond at all to photons having energy less than the bandgap energy, and incident electromagnetic energy in excess of the bandgap energy is wasted in the energy conversion. Therefore, the energy conversion efficiency of the semiconductor device is low, on the order of 25% or less. Therefore, it would be desirable to achieve effective solar energy conversion using materials other than semiconductors.
One possible alternative to semiconductors is the use of a metal-insulator-metal (MIM) configuration1-6. The MIM configuration is relatively inexpensive to manufacture in comparison to semiconductor-based systems. The native oxides of the metals are generally used as the insulator materials, therefore the MIM configuration is straightforward to fabricate. Efforts have been made even as recently as 1998 (See Ref. 6) to improve the characteristics of MIM devices, without substantially modifying the basic MIM configuration. Recent research in this area include efforts to use the MIM configuration to potentially provide devices capable of detecting and mixing signals at optical frequencies at optical communications wavelengths.
Turning now to the drawings, wherein like components are indicated by like reference numbers throughout the various figures, attention is immediately directed to FIGS. 1A-1E. FIGS. 1A-1E illustrate the operation of an MIM device for reference purposes. As a simplified configuration, an MIM device is illustrated in FIG. 1A. The MIM device, generally indicated by reference number 10, includes first and second metal layers 12 and 14, respectively, with an insulator layer 16 positioned therebetween. A corresponding energy band profile 20 is shown in FIG. 1B. Energy band profile 20 represents height of the Fermi level in the metals and the height of the conduction band edge in the insulator (y-axis 22) as a function of distance (x-axis 24) through MIM device 10 in the absence of provided voltage across the device. FIG. 1C illustrates a first modified energy band profile 30 when a voltage is provided in a reverse direction to MIM device 10. The voltage may be provided by, for example, an applied external voltage or an induced voltage due to the incidence of electromagnetic energy. In this case, tunneling of the electrons (not shown) can occur in a reverse direction, represented by an arrow 36. In contrast, as shown in FIG. 1D, when a voltage is provided in a forward direction to MIM device 10, a second modified energy band profile 40 results. In the case of the situation shown in FIG. 1D, tunneling of the electrons can again occur but in a forward direction, represented by an arrow 46. FIG. 1E illustrates a typical I-V curve 50 of current (y-axis 52) as a function of voltage (x-axis 54) for MIM device 10. I-V curve 50 demonstrates that the MIM device functions as a rectifying element. An MIM device provides rectification and energy detection/conversion by tunneling of electrons between first and second metal layers 12 and 14.
Continuing to refer to FIGS. 1A-1E, in energy conversion applications, it is further desirable to achieve high degrees of asymmetry and nonlinearity and sufficiently high current magnitudes in the current-to-voltage performance (I-V curve). If the current magnitude is too low, the incident electromagnetic energy will not be collected with high efficiency. The required current magnitude is a function of the MIM device geometry, dielectric properties of the oxide, and the size and number of the incident electromagnetic energy quanta. A higher degree of asymmetry in the I-V curve between positive values of V (forward bias voltage) and negative values of V (reverse bias voltage) about the operating point results in better rectification performance of the device. In addition, the differential resistance of the device, which influences the responsivity and coupling efficiency of the device to incoming electromagnetic energy, is directly related to the nonlinearity of the I-V curve. An optimal value of differential resistance is required to impedance match the MIM device to the antenna resulting in maximum power transfer to the device. The differential resistance of MIM devices are often too large for energy conversion applications and, consequently, it is desirable to lower differential resistance values in order to impedance match the antenna. In other words, in solar energy conversion applications, it is preferable to have a higher degree of nonlinearity in the I-V curve and optimal value of differential resistance in the device, thus yielding higher sensitivity of the device to incoming solar energy. As a result, high degrees of asymmetry and nonlinearity in the current-to-voltage characteristics of the device yields high efficiency in the energy conversion process. Currently available MIM devices are not able to provide sufficiently high degrees of asymmetry and nonlinearity with sufficiently low differential resistance in the current-to-voltage performance, hence the energy conversion efficiency of MIM devices is low.
A known alternative to the simple MIM device is a device with additional metal and insulator layers, as demonstrated by Suemasu, et al. (Suemasu)7 and Asada, et al. (Asada).8 The devices of Suemasu and Asada have the configuration of MIMIMIM, in which the three insulator layers between the outer metal layers act as a triple-barrier structure. The insulator layers are crystalline insulator layers formed by an epitaxial growth procedure detailed in Ref. 7. The presence of the barriers between the outer metal layers result in resonant tunneling of the electrons between the outer metal layers under the appropriate bias voltage conditions, as opposed to simple, tunneling of the MIM device. The resonant tunneling mechanism in the electron transport yields increased asymmetry and nonlinearity and reduced differential resistance values for the MIMIMIM device. The resonance tunneling also results in a characteristic resonance peak in the current-voltage curve of the device, which yields a region of negative differential resistance and leads to the possibility of optical devices with very fast responses and high efficiency.
However, the MIMIMIM devices of Suemasu and Asada have the distinct disadvantage of being a much more complicated device than the simple MIM device. The fabrication procedure of Suemasu includes the deposition of cobalt, silicon and calcium fluoride to form alternating layers of CoSi2 and CaF2. These rather exotic layer materials were chosen due to the crystalline lattice matching constraints inherent in the epitaxial growth procedure. Several of the difficulties in the fabrication procedure, such as the problem with agglomeration of cobalt on the CaF2 layer as well as the multiple photolithography and selective etching steps required to form the final device after the MIMIMIM layers have been grown, are described in Ref 7. Suemasu also contends that the use of a triple-barrier structure, rather than a slightly simpler double-barrier structure, is necessary in order to achieve negative differential resistance resulting from resonant tunneling using only metal and insulator layer combinations, thus avoiding the use of semiconductor materials. In addition, Suemasu requires that the thickness of the individual metal and insulator layers must be strictly controlled to the atomic layer level in order to achieve the resonance tunneling effect. Therefore, although the goal of increased nonlinearity and asymmetry may be achieved in the MIMIMIM devices of Suemasu and Asada using metal and insulator combinations, the simplicity of the MIM structure is lost.
An alternative device structure that has been suggested to achieve resonant tunneling in semiconductor devices is the use of two adjacent insulator layers between two semiconductor layers, resulting in a semiconductor-insulator-insulator-semiconductor (SIIS) structure described by Papp, et at (Papp).9 Papp describes a theoretical SIIS structure, in which the two crystalline insulator layers are formed of two different insulator materials by crystal growth techniques. The SIIS structure is said to yield a resonant tunneling effect with negative differential resistance, increased nonlinearity and asymmetry as well as negative differential resistance, similar to that shown in the aforedescribed MIMIMIM devices of Suemasu and Asada, although an actual SIIS structure has not yet been implemented, to the Applicants"" knowledge. Current crystal growth techniques theoretically enable the implementation of the SIIS structure, but an SIIS device would still embody the drawbacks inherent in semiconductor materials, namely cost efficiency in large area devices. In addition, Suemasu (see Ref. 7) speculates that the recent trend of decreasing the size of electronic devices in order to achieve high speed switching will make semiconductor-based devices impractical due to fluctuation of carrier concentration, which occurs when semiconductor devices are reduced to mesoscopic regimes.
The energy which is detected and converted by the MIM diode can be delivered to the diode by means of an antenna as described by Fumeaux et al. in [6]. The antennas used at infrared frequencies are typically planar since they are fabricated using semiconductor fabrication techniques such as metal evaporation and patterning. The bow-tie antenna, in particular, is a popularly used antenna for infrared detectors since it is broadband and less susceptible to fabrication tolerances than a dipole antenna. The detected signal is extracted from the diode by using low frequency leads. In previous work, low frequency leads have been connected across the bowtie antenna center terminals where the diode is connected, or across the entirety of the outermost edges of the antenna arms. The former, which will be referred to as the center-fed arrangement is presented by Fumeaux et. al. [6]. The latter edge-fed arrangement is shown in one paper by Rutledge and Muha et. al. [10] as well as in another paper by Rutledge et al. [11]. As will be described at appropriate points below, the present invention recognizes certain problems with both the center-fed arrangement and the edge-fed arrangement which are thought to be unresolved by the prior art.
As will be seen hereinafter, the present invention provides a significant improvement over the prior art as discussed above by virtue of its ability to provide the increased performance while, at the same time, having significant advantages in its manufacturability. This assertion is true for electromagnetic devices generally, which take advantage of the present invention, as well as solar energy conversion devices in particular. Moreover, certain problems relating to prior art center-fed and edge-fed configurations are thought to be resolved.
1. J. G. Simmons, xe2x80x9cElectric tunnel effect between dissimilar electrodes separated by a thin insulating film,xe2x80x9d Journal of Applied Physics, 34 (1963).
2. S. R. Pollack and C. E. Morris, xe2x80x9cElectron tunneling through asymmetric films of thermally grown Al2O3,xe2x80x9d Journal of Applied Physics, vol. 35, no. 5 (1964).
3. L. O. Hocker, et al., xe2x80x9cFrequency mixing in the infrared and far-infrared using a metal-to-metal point contact diode,xe2x80x9d Applied Physics Letters, vol. 12, no. 12 (1968).
4. S. M. Faris, et al., xe2x80x9cDetection of optical and infrared radiation with DC-biased electron-tunneling metal-barrier-metal diodes,xe2x80x9d IEEE Journal of Quantum Electronics, vol. QE-9, no. 7 (1973).
5. B. Michael Kale, xe2x80x9cElectron tunneling devices in optics,xe2x80x9d Optical Engineering, vol. 24, no. 2 (1985).
6. C. Fumeaux, et al, xe2x80x9cNanometer thin-film Nixe2x80x94NiOxe2x80x94Ni diodes for detection and mixing of 30 THz radiation,xe2x80x9d Infrared Physics and Technology, 39 (1998).
7. T. Suemasu, et al., xe2x80x9cMetal (CoSi2)/Insulator (CaF2) resonant tunneling diode,xe2x80x9d Japanese Journal of Applied Physics, vol. 33 (1994).
8. M. Asada, et al., xe2x80x9cTheoretical analysis and fabrication of small area Metal/Insulator resonant tunneling diode integrated with patch antenna for terahertz photon assisted tunneling,xe2x80x9d Solid State Electronics, vol. 42, no. 7-8 (1998).
9. G. Papp, et al., xe2x80x9cCurrent rectification through a single-barrier resonant tunneling quantum structure,xe2x80x9d Superlattices and Microstructures, vol. 17, no. 3 (1995).
10. Rutledge, D. B., and Muha, M. S., xe2x80x9cImaging Antenna Arrays,xe2x80x9d IEEE Trans. On Antennas and Propagation, Vol. AP-30, 1982, pp. 535-540.
11. Rutledge, D. B., Neikirk, D. P., and Kasilingam, D. P., Chapter 1, page 25, xe2x80x9cInfrared and Millimeter Waves,xe2x80x9d Vol. 10, Edited by Kenneth J. Button.
As will be described in more detail hereinafter, there is disclosed herein an electron tunneling device including first and second non-insulating layers. The first and second non-insulating layers are spaced apart from one another such that a given voltage can be provided across the first and second non-insulating layers, either by an applied external bias voltage or, for example by an induced voltage due to the incidence of solar energy without an applied voltage or both. The electron tunneling device further includes an arrangement disposed between the first and second non-insulating layers and configured to serve as a transport of electrons between the first and second non-insulating layers. This arrangement includes a first layer of an amorphous material configured such that using only the first layer of the amorphous material in the arrangement would result in a given value of a first parameter in the transport of electrons, with respect to the given voltage. However, in accordance with one aspect of the invention, the arrangement includes a second layer of material, which second layer is configured to cooperate with the first layer of amorphous material such that the transport of electrons includes, at least in part, transport by a mechanism of tunneling, and such that the first parameter, with respect to the given voltage, is increased over and above the given value of the first parameter. The first parameter is, for example, nonlinearity or asymmetry in the electron transport.
In another aspect of the invention, the first layer of amorphous material, if used alone in the arrangement of the electron tunneling device, would result in a given value of a second parameter in the transport of electrons, with respect to the given voltage, but the second layer of material is also configured to cooperate with the first layer of amorphous material such that second parameter in the transport of electrons, with respect to the given voltage, is reduced below the given value of the second parameter. The second parameter is, for example, differential resistance.
In yet another aspect of the invention, a device for converting solar energy incident thereon into electrical energy is described. The device has an output and provides the electrical energy at the output. The device includes first and second non-insulating layers spaced apart from one another such that a given voltage can be provided across the first and second non-insulating layers. The device also includes an arrangement disposed between the first and second non-insulating layers and configured to serve as a transport of electrons between the first and second non-insulating layers. The arrangement includes a first layer of an amorphous material. The arrangement also includes a second layer of material configured to cooperate with the first layer of the amorphous material such that the transport of electrons includes, at least in part, transport by a mechanism of tunneling, and such that the solar energy incident on the first and second non-insulating layers, at least in part, is extractable as electrical energy at the output.
In a further aspect of the present invention, an assembly includes a device configured for receiving at least one input to produce an output responsive thereto. An antenna arrangement supports the device to transfer the input to the device and further to transfer the output from the device such that the antenna arrangement supports a selected one of the input and the output as a high frequency current and the antenna arrangement includes a peripheral configuration which confines the high frequency current to at least one dominant path within the antenna arrangement so that the high frequency current oscillates in the dominant path and so that the other one of the input and the output is a lower frequency signal that is present at least generally throughout the antenna arrangement. At least one port, within the antenna arrangement, is positioned sufficiently away from the dominant path so as to isolate the lower frequency signal at the port from the high frequency current in the dominant path.
In a continuing aspect of the present invention, an assembly includes a device configured for receiving at least one input to produce an output responsive thereto. An antenna arrangement supports the device to transfer the input to the device and further to transfer the output from the device such that the antenna arrangement supports a selected one of the input and the output as a high frequency current and the antenna arrangement includes a peripheral configuration which confines the high frequency current to at least one dominant path within the antenna arrangement and the other one of the input and the output is a lower frequency signal that is present at least generally throughout the antenna arrangement. At least one port, within the antenna arrangement, at a location selected such that the high frequency current travels past the port in at least one direction that is away from the device, and the port is positioned sufficiently away from the dominant path so as to isolate the lower frequency signal at the port from the high frequency current in the dominant path.
In an additional aspect of the present invention, an assembly includes a device configured for receiving at least one input to produce an output responsive thereto. An antenna arrangement supports the device to transfer the input to the device and further to transfer the output from the device such that the antenna arrangement supports a selected one of the input and the output as a high frequency current and the antenna arrangement includes a peripheral configuration which confines the high frequency current to at least one resonant path within the antenna arrangement so that the high frequency current oscillates in the resonant path between a pair of opposing first and second reflector configurations that are formed as part of the peripheral outline and so that the other one of the input and the output is a lower frequency signal that is present at least generally throughout the antenna arrangement. At least one port, within the antenna arrangement, which port is positioned sufficiently away from each one of the first and second reflector configurations so as to sustain reflection of the surface current in the resonant path while conducting the lower frequency signal.
In another aspect of the present invention, an assembly includes a device configured for receiving at least one input to produce an output responsive thereto. An antenna arrangement includes a bowtie peripheral configuration defining a bowtie intersection for supporting the device at the bowtie intersection to transfer the input to the device and further to transfer the output from the device such that the antenna arrangement supports a selected one of the input and the output as a high frequency current and the bowtie peripheral configuration confines the high frequency current to at least one dominant path within the antenna arrangement so that the high frequency current oscillates in the dominant path traveling through the bowtie intersection and so that the other one of the input and the output is a lower frequency signal that is present at least generally throughout the antenna arrangement. At least one port, within the antenna arrangement, is positioned spaced apart from the bowtie intersection and sufficiently away from the dominant path or paths so as to isolate the lower frequency signal at the port from the high frequency current in the dominant path.
In a related feature, an assembly produced in accordance with the present invention may be configured for operation in any one of a modulation mode, a mixing mode, a detection mode and an emitting mode dependent upon the type of active device that forms part of the assembly.